The downstream faces and spillways of dams are subject to severe damage from large volumes of water flowing rapidly over the dam, from debris carried with the water, and from exposure to extreme variations of temperature. To repair or modify the downstream face or spillway often requires work to be done under water and it is highly desirable to eliminate, reduce or otherwise control the flow of water over the dam in the area of the surfaces to be repaired so that divers or other workmen can work safely in the area.
It has been necessary in the past, in those instances where the dam was not equipped with permanent gates, to install temporary gates along the crest of the dam to restrict or block the flow of water in the area of the gate, the gates being secured to the dam with structural fittings. Frequently it was necessary to install these temporary gates while water flowed at high velocity over the crest of the dam. This is an expensive and dangerous procedure. I have found that this expense and danger can be largely avoided by use of my invention.
Apart from temporary gates fixed to the dam, conventional techniques have also utilized barges which are floated against the upstream side of the dam in an attempt to divert the water around the area of the workers immediately downstream of the dam and to minimize the water flowing over the dam in that area. This presents problems in that the barge or float must have sufficient depth to hold it against the dam and even then may float over the dam with rising waters. Often the wind and/or flowing water makes it difficult to keep the barge in position for blocking the flow of water over the dam and to keep the barge from floating over the dam.
Another technique for quieting waters for workmen is shown in U.S. Pat. No. 901,104. This patent utilizes a cassion which forms an enclosure for a work area on the bottom of the water body. The enclosure is lowered from an interior well of a floating barge or vessel and has a movable lower wall portion for forming the lower part of each side. This part is movable with and relative to an upper wall portion for that side.